As the Beatles expanded their horizons, Paul McCartney, more than the others, took an interest in classical music, which resulted in producer George Martin's string arrangements for songs like “Yesterday” and “Eleanor Rigby.” But it wasn't until 1991 that he debuted his first full-length symphonic composition, Liverpool Oratorio, a collaboration with composer/conductor Carl Davis.

“I prefer to think of myself as a primitive, rather like the primitive cave artists who drew without training,” McCartney said at the time. “Hopefully, the combination of Carl’s classical training and my primitivism will result in a beautiful piece of music. That was always my intention.

Davis and McCartney had become friends in the late ’80s, as the Royal Liverpool Philharmonic Orchestra was seeking a special composition to mark its 150th anniversary. The orchestra’s programmer was picking Davis’s brain for ideas when the composer suggested a collaboration with McCartney, who – as a former Beatle – was possibly the most famous product of the English city.

“They only asked us for something for their 150th anniversary of the orchestra, you know. We could have just given them a little string quartet, three minutes … thank you very much and happy birthday,” McCartney said when creating this piece. “It’s only just beginning to dawn on me that we’ve bitten off something fairly big here: one-and-a-half hours, eight movements with the full kitchen sink.”

The “full kitchen sink” meant that McCartney and Davis’s epic composition would include the city’s orchestra, multiple choirs and world-famous soloists, all to be performed at the Liverpool Cathedral. It would be titled the Liverpool Oratorio, an oratorio being a work that combines orchestra and voices with a narrative that reflects a spiritual theme – for instance, Handel’s Messiah.

McCartney didn’t make himself the messiah in the Liverpool Oratorio, but he did draw on his upbringing in the blue-collar city. The piece’s protagonist, Shanty, is born in Liverpool in 1942, the same year as Paul. McCartney’s school motto -– “Not for ourselves but for the whole world” -- is part of the lyrics and an entire movement revolves around Shanty’s father, reflecting the closeness between Paul and his dad.

Some of the religious motifs surround the father’s funeral, as well as the oratorio’s happy ending, when the chorus and soloists declare “God is good.” McCartney said he left out any references to Jesus to make the oratorio inclusive of people of various faiths. “The work evolved over a long time because Paul was touring,” Davis recalled years later. “Throughout our meetings he was curious about the process, but I felt to some extent he pretended he didn’t know as much as he did.”

The Liverpool Oratorio was ready for its grand unveiling for the RLPO’s 150th anniversary celebration in 1991. With McCartney in the audience and Davis conducting, the performances on June 28 and 29 were filmed and recorded (causing a temporary black-out in the cathedral on premiere night due to all the generators). A two-disc album was released on Oct. 7, 1991, in Britain, and Oct. 22 in the States.

The premiere was a success, and the piece went on to be performed around the world. The album, meanwhile, topped the classical charts in both the U.K. and U.S., even making an appearance on the pop album charts in both countries (No. 36 U.K., No. 177 U.S.).

Although the album fared well commercially (for a classical release), it failed to impress the music press. While some felt that McCartney was trying to moonlight as a “serious musician,” others thought the work was overlong, derivative and lacking in the lyrical department.

For his part, McCartney appeared to enjoy his crash course in classical with Davis, who continued to work on film and television scores, as well as helm an orchestral album of Beatles tunes. With one classical album under McCarrtney’s belt, the rock star began to work on other symphonic material intermittently with his pop albums.